The separation of molecular species using gel electrophoresis methods is well known in the art. Various molecular species, including, inter alia, proteins, peptides, oligonucleotides, DNA and RNA may be electrophoretically separated on a body of separating gel, based, inter alia, on their charge/mass ratio, dimensional characteristics and other properties. Methods of isoelectric focusing may also be used for molecular species separation, as is well known in the art.
It is often necessary or desired to transfer the electrophoretically separated molecular species or resolved components from the separating gel into another matrix or onto a support in order to perform additional desired steps or chemical reactions, or immunological characterization or other manipulations on the separated molecular species. A useful method known in the art for transferring such resolved or separated species from the gel into another matrix or onto a support is electro-blotting.
A review article entitled “Protein Blotting: A review” by B. T. Kurien and R. H. Scofield published in J. of Immunological methods, Vol. 274, pp. 1-15 (2003), incorporated herein by reference in its entirety, describes, inter alia, various protein blotting methods including wet and semi-dry electro-blotting methods.
U.S. Pat. Nos. 5,482,613, 5,445,723, 5,356,772, 4,889,606, 4,840,714, 5,013,420, and US Published Application 2002157953 disclose, inter alia, various types of apparatuses and methods for performing wet and semi-dry electrophoretic transfer, all the above cited US Patents and published Patent Application are incorporated herein by reference in their entirety.
In electro-blotting, after electrophoretic separation of molecular species, the electrophoresis gel containing the separated molecular species is put in contact with a relatively thin matrix of a porous material, such as, among others, a nitrocellulose-based blotting membrane, a PVDF-based blotting membrane, an activated paper blotting membrane, an activated nylon blotting membrane or the like, and an electrical current is passed through the sandwiched gel and blotting membrane in a direction generally perpendicular to the surface of the blotting membrane. Some or most of the electrically charged molecular species may thus be electrophoretically transferred from the gel to the blotting membrane.
Current may be passed through the gel and blotting membrane combination by putting the gel and the blotting membrane between two suitable electrodes and applying a suitable voltage difference between the electrodes. One such electrode operates as a cathode and the other opposite electrode operates as the anode.
Typically, the electrical connection between the electrodes and the gel and blotting membrane is achieved by placing an electrically conducting buffer solution between the electrode and the gel and/or between the electrode and the blotting membrane. These buffer solution(s) serve as a source of ions for the electro-blotting. This method is known in the art as wet blotting. A disadvantage of wet blotting methods is the need for relatively cumbersome apparatus and the need to prepare and handle buffers, thus making the method time consuming.
Alternatively, one or more pieces of dry filter paper or another suitable type of dry porous material are put in contact with the blotting membrane and with the gel, the filter paper or other dry porous material is wetted with a buffer solution that serves as the ion reservoir for the transferring. The electrodes (cathode and anode) are put in contact with the buffer wetted filter paper(s) or other porous material and electro-blotting is performed.
While the semi-dry electro-blotting methods known in the art solve some of the problems of wet electro-blotting methods, they still have the disadvantage of requiring preparation and handling of liquid buffer solutions for wetting the filter papers and requiring handling and alignment of the filter papers with the gel and the blotting membrane. These methods are, therefore, still inconvenient and time consuming. Additionally, in semi-dry electro-blotting methods, the limited amount of ions in the buffer wetted filter paper may limit the amount of current that may be used, resulting in a relatively long electro-blotting time. Commercially available semi-dry blotters are typically limited to current densities in the range of 2-6 milliamperes per square centimeter (2-6 mA/cm2).